# Cryptography

**Cryptography** is the science of encoding and decoding data securely.

**Encryption** is a process by which data readable to anybody (known as *plaintext*) is converted by a mathematical process into a form that can only be decoded and understood by the holders of a particular *key* (known as *ciphertext*). This key usually takes the form of a large numerical value, although it may be represented by a word or phrase for ease of memory and transmission.

Two broad types of encryption are:

- Symmetric-key cryptography
- Public-key cryptography

With the symmetric-key version, the same key or password is used to encrypt and decrypt the data. With a public-key or asymmetric cipher, one key is used for encryption and another for decryption. The encryption key is often publically available, while the decryption is held private by the recipient.

**Decryption** reverses this process so that formerly encrypted data may be accessed as plain data.